The invention is based on a fuel injection pump. In an injection pump of this type, known from German Offenlegungsschrift No. 19 19 969, the fuel quantity which is to be injected during the supply stroke of the pump piston of the injection pump is metered during the suction stroke of the pump piston by means of the magnetic valve, which is controlled either in increments or in analog fashion. The metered quantity is determined by the opening time of the magnetic valve, the opening phase of this valve being located exclusively within the period of the suction stroke of the pump piston. In this known apparatus, pressure conditions in the work chamber of the fuel injection pump influence the metered quantity. Depending upon the instant of opening of the magnetic valve, a more or less reduced pressure prevails in the work chamber. For precise metering of the fuel injection quantity, the rpm and the instant of injection must be taken into consideration in this known apparatus in order to set the opening times of the magnetic valve. Pressure fluctuations in the work chamber during the fill process must also be considered. Further disadvantages are associated with the limited speed of switching of the magnetic valve. The two switching processes of the magnetic valve which take place during the metering phase thus affect the precision of the product of metering. Furthermore, there are limits on the rpm or the rotary speed of the injection pump because of the switching time of the magnetic valve.
In another fuel injection pump, known from German Offenlegungsschrift No. 19 19 707, the limited switching speed of magnetic valves is taken into consideration by accommodating two pumping systems in the distributor in this distributor-type pump. Each pumping system is supplied with fuel by way of a magnetic valve. In this manner, an increased pump rpm can be obtained. Furthermore, the cam drive of the pump pistons in this injection pump is designed such that the stroke speed of the pump piston during the suction stroke is much less than that during the supply stroke of the pump pistons. The magnetic valve of each pumping system of this radial-piston pump is also opened exclusively during the suction stroke of the pump pistons, and the opening duration of the magnetic valve determines the metered quantity. Here again, the rpm and the adjustment of injection time must be taken into consideration in controlling the magnetic valves. In designing this pump, the metering cycle of the magnetic valve begins with the suction stroke of the associated pump pistons. An adjustment of injection onset dictates a change in the onset of the suction stroke, so that this suction stroke onset must be provided precisely when calculating the opening time of the magnetic valve. Furthermore, dynamic conditions at the reversal point of the pump piston, that is, at the transition from the supply stroke to the suction stroke, are difficult to control.